1. Field of the Invention
The invention disclosed herein relates to the surface on a contact element such as found in card edge connectors which make electrical contact with the conductive trace or pad on a circuit card inserted in the connector.
2. Prior Art
Contemporary contact elements are formed to provide a convex surface adjacent the upper free end. U.S. Pat. Nos. 3,665,370, 4,077,688 and 4,303,294 disclose such contact elements. The convex surface is plated with gold as is the trace on the circuit card against which the convex surface abutts. The gold plating provides a tough surface capable of withstanding sliding motion between the two abutting surfaces. Less noble plating; e.g., tin, wears away quickly under sliding motion, including such motion induced by thermal expansion and contraction, and the resulting fretting corrosion causes reduced electrical contact between the abutting surfaces. Accordingly, such plating, although less expensive and having adequate electrical properties, have been relegated to stationary contacts which are preferably under substantial compression to prevent movement. U.S. Pat. No. 3,853,382 discloses one such successful application of non-noble plating.